Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a fluid sampling system for effecting the transfer of samples of a second fluid from a body of that fluid into a system incorporating an enclosed volume of a first fluid. The first fluid may or may not circulate within the system.
2. Description of the Background Art
Such fluid sampling systems are commonly employed in analytical instruments e.g. chromatographs and mass spectrometers where it is needed to transfer for analysis a small ample of gas, vapor or liquid of interest.
Such fluid sampling systems may also be employed, for example, in atmospheric monitoring or analysis equipment where a sample or samples of an ambient atmosphere are to be transferred into a closed loop circulatory system within the equipment and examined for the presence of components of interest.
Atmospheric monitoring equipment of this general type is described in UK Patent No. 2052750 in which an external atmosphere is sampled by drawing a flow of the external atmosphere over a membrane through which a sample of the atmosphere permeates into a closed loop circulatory system and is entrained in the closed loop gas flow, and conveyed to means for detecting and/or identifying vapors or gases of interest in the entrained sample.
Membrane inlet systems, such as employed in the equipment described in UK Patent No. 2052750, suffer a number of significant disadvantages. For example the membrane employed in such systems has a slow response to sampling commands, tends to retain sample from one sampling to the next, and often requires local heating to optimize sample permeation through it. Most inconveniently the transmission characteristics of the membrane cannot be varied, for example to permit variation of instrumental sensitivity or dynamic measurement range.
It is an object of the present invention to provide a novel fluid sampling system in which the disadvantages of such prior art sampling systems are largely overcome or at least mitigated.
According to an aspect of the present invention there is provided a fluid sampling system for extracting a fluid sample from a body of fluid, the system comprising fluid enclosing means arranged to enclose a volume of a first fluid into which the sample of a second fluid is to be introduced, the fluid enclosing means comprising a substantially closed chamber including a wall generally separating the first fluid from the second fluid, and a pin-hole aperture disposed thereon via which the second fluid may be drawn into the fluid enclosing means, and means for drawing a sample of the second fluid into the body of the first fluid through the pin-hole aperture, comprising pressure pulse means arranged to apply a negative pressure pulse to the first fluid and in which the negative pulse applied to the first fluid is applied directly to the second fluid via the pin-hole aperture, whereby a differential pressure is caused to exist across the pin-hole aperture.
Continuous transfer may be effected by applying a repetitive pressure pulsing to the system incorporating the enclosed fluid volume.
Although repetitive pulsing will cause fluid flow through the orifice from the body of the fluid into the enclosed fluid volume and vice versa, sample material incoming to the enclosed fluid volume will be impelled into the enclosed fluid volume or, in the case of there being a circulatory flow within the system incorporating the enclosed fluid volume, will be entrained in the flow and conveyed away from the orifice, resulting in each case in a net flow of sample fluid into the enclosed fluid volume.
The rate at which sample material is transferred through the orifice may be controlled by variation of the amplitude, the repetition rate, or the duration of, the pressure pulses, or by a combination of two or more of those parameters.
The rate of transfer of sample material through the orifice may be controlled automatically by controlling one or more of the parameters of the pressure pulses applied to the system incorporating the enclosed fluid volume in response to a measured value of the transferred fluid sample or of a component of interest in the transferred fluid sample.
The pressure pulses applied to the system incorporating the enclosed fluid volume may be generated by means of an electromechanical transducer in which an applied electrical signal generates a mechanical displacement capable of producing pressure pulsing of the system. By varying the characteristics of the electrical drive signal to the transducer, the parameters of the pressure pulses may be similarly varied.
The electromechanical transducer may be such as to produce variations in the system by positional variation of a diaphragm in response to the electrical signal applied to means displacing the diaphragm.
Such a transducer may be mounted in the system incorporating the enclosed fluid volume with the diaphragm in direct contact with the fluid in the system thereby enabling pressure pulses to be applied directly to the fluid.